The occurrence of ventricular fibrillation after aortic de-clamping during cardiac surgery is common, and if prolonged may contribute to myocardial ischaemia. The use of lignocaine cardioplegia to minimize reperfusion ventricular fibrillation was studied in 141 patients undergoing first time coronary artery surgery in a double blind prospective randomized trial: 71 patients received lignocaine 100 mg/l in their cardioplegia, whereas a control group of 70 patients received cardioplegia without lignocaine. Lignocaine cardioplegia reduced significantly the incidence of reperfusion ventricular fibrillation from 63% to 42%. Of those patients developing reperfusion ventricular fibrillation, a higher proportion receiving lignocaine cardioplegia underwent spontaneous defibrillation (30% vs 11%) though this was not statistically significant. The incidence of atrio-ventricular (A-V) block necessitating ventricular pacing to separate from cardiopulmonary bypass was significantly higher in the lignocaine treated group (44%) than in the control group (20%): this may have been due to the additive effect of procaine in the cardioplegia solution. In the majority of cases this A-V block was transient and had resolved prior to the completion of surgery.